Abrasive article



Patented May 18, 1943 PATENT @FHEE ABMSWE AR'ii'liClLlE Jacob liiui'ta, Teanech, N. 3., assignor to Callite Tungsten @orporation, Union City, N. 3., a corporation of Delaware 7 Claims.

The present invention relates to improvements in lapping and grinding devices. More particularly, it relates to diamond laps and diamond or other abrasive bearin grinding wheels and to an improved method of making the same.

Diamond and various abrasive materials are at present used extensively in dressing tools, for grinding wheels and core bits for rock drilling and many similar uses. It is frequently the case, however, that the diamonds or other abrasives are so insecurely set and bonded into their mountings that they work loose and come out, and in such case there is a tendency for the surface of the wheel to glaze. A glazed wheel inhibits the cutting qualities of the abrasive particles and, furthermore, tends to overheat.

It is an object of the present invention to provide a grinding element or laphaving superior cutting and polishing properties. It is a further object or the invention to provide a: method of securely bonding diamond and other abrasive particles in a, mount composed of materials that will securely hold the abrasives in place and that will selectively wear down in use to a sufilcient degree to permit ever fresh exposure of sharp abrasive particles to the worlr piece. In this way the greatest economy is achieved. The material of which the amount is composed is of such a nature and is compounded in such a manner that it will completely surround the abrasive grain particles in close and tenacious contact and will hold them firmly and at the same time it has sufficient high strength to withstand maximum peripheral speed without glazing, overheating, or excessive wear.

. In. carrying out the invention I first provide an abrasive grain that has as its foundation the true abrasive material, a grit consisting of diamond, silicon carbide, boron carbide, sapphire, or the like in finely divided form. This foundation abrasive grit is coated with metallic and glass or ceramic coatings in the manner hereinafter described to form the abrasive grain. The abrasive or cutting article of the invention is then made by forming the abrasive grain, mixed with powdered bonding metal appropriate to the contemplated use, into the desired shape under high pressure and sintering to a very compact unit. The abrasive article so formed may then be treated with a hydrolized silicic acid ester so as to fill all the pores. The finished article resulting is a strong abrasive unit having the abrasive material firmly bonded into the mount and sumciently strong to resist glazing, overheating or wear.

In carrying out the invention I proceed in the following manner:

I first treat the abrasive grit with a. concentrated solution of an easily reducible metallic salt such as silver or copper nitrate. The grit is wetted with a measured amount of this solution,

d outlined above.

(Ci. Erik-293) 5 coat this metallic coated abrasive grit with a glass or ceramic coating in the following manner: I prepare a mixture of finely divided silica, alumina, thoria, zirconia or the like, and an alcoholic solution or suspension of boric enhydride, sodium lil carbonate, sodium borate, and finely divided talc.

Hereinafter I refer to this mixture as Mixture A. To this mixture I add the abrasive grit coated with metal as above described. The grit and the ingredients of Mixture A are thoroughly mixed l5 and the whole is then carefully dried, stirred to prevent lumpy formations, and then heated to a temperature just to or slightly below the fusing temperature of Mixture A so as to cause a partial fusion and sintering of the ingredients of Mixture A around the particles of the abrasive grit.

This'partially sintered mass is then broken or crushed to a mesh size which is determined by the use to which the final article is to be put, the particle sizes being slightly larger than those of the particles of the original abrasive grit. This ceramic or glass coated grit is then again treated with metallic nitrates as above described, in order to produce a firmly bonded metallic coating on its surface. This is the abrasive grain.

An alternative method of forming the abrasive grain consists in making a specially prepared glass or ceramic by fusing a mixture of boric oxide, aluminum oxide, silicic acid, zirconium and thorium oxide. This glass is then crushed,

I ground and sifted to obtain a. glass powder of a mesh size suitable to the purpose desired. It may be said in general that a, very fine powder gives much better bonding qualities. This glass powder and the abrasive grit above described are thoroughly mixed. The whol mixture is then heated to such a temperature that the glass fuses" and forms a very adhering film around the particles of the abrasive grit. Here again this glass coated abresive grit is coated with a metallic coating as This coating of metal and glass is of service later in forming a secure bond and anchor of the abrasive particles in the mount. The result is the abrasive grain, and either this or the abrasive grain described in the first ex- 59 ample may be used for incorporation in the material forming the mount.

The mount is formed in the following manner.

The abrasive grain and the metal powder are thoroughly mixed together. This may be done by rolling and tumbling the mixture in a jar mill for such a period of time and at such a speed as to produce a uniformly distributed mixture. The metal powder so added may be silver, copper, cobelt, manganese, chromium, aluminum or mix- 60 tures or alloys of these materials, or they may the degree of porosity of the abrasive article.

- be powdered metal of the refractory group consisting of tungsten, molybdenum and tantalum, or their carbides,'with additions of copper, silver and nickel, cobalt or iron depending on the use to which the finished abrasive article is to be put. The main consideration in choosing the metals so to be added is thatthey should be capable of producing, under proper heat treatment, the finely sintered and fully compacted unit free from excess of porosity and oxide formation.

The particular metal powder chosenor the combination of metals will dictate the manner of heat treatment. For example, when using silver the heat treatment may be carried out in a ceramic container, the compressed parts being covered with a little carbon powder and heated in a gas-fired or electric furnace. The carbon powder will thus prevent any excessive oxidation of the metallic or non-metallic aggregates.

When tungsten or molybdenum are used, the compressed abrasive particles may be heat treated in an atmosphere of inert gases, such as dry hydrogen, nitrogen or argon, or in a special vacuum'furnace wherein the abrasive particles may be heated under partial pressure of air, hydrogen, nitrogen, etc.

The abrasive grain and metal powder being thus thoroughly mixed is shaped in a die under hydraulic pressure and is then sintered at elevated temperatures. The result is a densely compacted grinding device or lap.

As a final step, the abrasive article thus formed is preferably treated with'a solution of a partially hydrolized silicic acid ester such as ethyl orthosilicate commonly known as ethyl silicate, in a manner to fill all the pores. The abrasive article is then allowed to dry slowly and is finally heated to complete the bonding action.

This treatment with the partially hydrolized silicic acid ester may be varied depending upon It may be advantageous to treat the article in a vacuum to insure complete penetration and filling of all the pores in order to complete the bonding action.

By way of example, but not of limitation, I give the following formula of Mixture A, the proportions being by weight:

Boric oxide 15 Silica a- 50 Aluminum oxide 20 Magnesium oxide 5 Thorium oxide 2 Zirconium oxide 2 Talc 1 Sodium carbonate 3 Sodium borate 2 Mixture A and the abrasive grit prepared in the manner above described are then mixed in the following proportions to form the abrasive grain:

Per cent by weight Mixture A 33 Abrasive grit 67 Per cent by weight Treated abrasive grain 67 Metal powder 33 But this also may vary in accordance with the use to which the final article is to be put.

Having thus described my invention, what I claim is: I

1. The method of making an abrasive article which comprises preparing abrasive material in the form of a finely divided grit; coating said grit successively with metal, glass and again metal; mixing said grit so coated with powdered metal adapted to form a mount; pressing said mixture of grit and mount metal into desired form; sintering said form; and treating-the same with 'a solution of ethyl orthosilicate in a manner to fill the pores of said mount.

2. An abrasive grain suitable for mounting in an abrasive tool consisting of finely divided abrasive material coated first with metal of the group consisting of silver and copper, then with glass, and finely with a metal of the same group.

3. An abrasive grain suitable for mounting in an abrasive tool consisting of finely divided diamond grit coated first with silver, then with glass and finely with silver.

4. An abrasive grain suitable for mounting in an abrasive tool consisting of finely divided diamond grit coated first with copper, then with glass and finally with copper.

5. An abrasive article comprising an abrasive grain consisting of finely divided diamond grit coated first with copper, then with glass and finally with copper and mounted in a sintered metallic mount.

6. An abrasive tool comprising an abrasive grain consisting of finely divided abrasive material coated first with metal of the group consisting of silver and copper, then with glass and finally with a metal of the same group and mounted in a sintered metallic mount.

'7. An abrasive tool comprising an abrasive grain consisting of finely divided diamond grit coated first with silver, then with glass and finally with silver and mounted in a sintered metallic mount.

JACOB KURTZ. 

